SWS: dietary data collection

During the initial home visit and at 11- and 34-weeks’ gestation, research nurses assessed dietary intake during the preceding three months using a 100-item FFQ. The foods or food groups included in the FFQ were based on their ability to contribute at least 90% of the macronutrients, iron and vitamin C in the diet based on published data [125]. The women were also asked about the type and frequency of consumption of any food supplements at these three visits.

Women reported their average frequency of consumption of each food group using the following responses:

• (1) never
• (2) once every 2-3 months
• (3) once per month
• (4) once per fortnight
• (5) 1-2 time per week
• (6) 3-6 times per week
• (7) once a day
• more than once per day (with the option to specify the number of times per day).

Prompt cards with lists of foods included in food groups were used to ensure standardised responses. The amount of milk and sugar consumed daily over the last three months as well as the average portion size of bread and potatoes were also recorded. The frequencies of consumption of foods not listed on the FFQ were recorded if they were consumed ≥1x/week.

The 100-item FFQ was used during a home visit to record the dietary intake of the sub-group of non-pregnant women two years after the initial interview to assess stability of dietary patterns over time. In addition to the FFQ, participants were asked ‘Have there been any major changes to your diet since we saw you two years ago?’ and if ‘yes’, details of the changes were recorded.

At approximately 6 and 12 months of age, an FFQ and details of the child’s milk-feeding history over the prior six months as reported by their main caregiver (usually the mother) were recorded by research nurses. Breast milk intake was estimated from the reported duration of breast-feeding at each feed [126] and the age of introduction to solid foods was recorded.

The two infant FFQs to be used at age 6- and 12-months, were developed using a variety of dietary information sources. The list of foods to be included was compiled using information from a nationally representative sample of children aged 18 months [100], the weighed food diaries of preterm infants aged 6 and 12 months [127], infant-feeding literature and dietary data from women in Southampton [128]. This food list was refined after a 24-hour recall of a sample of infants and through piloting [129].

At 6 months old, a 34-item FFQ was administered to capture average frequency and amount of listed foods consumed over the seven days preceding the interview. Responses included the number of times the food/food group was consumed over the past week, the brand and amount consumed in household measured.

At 12 months of age, a 78-item FFQ was administered to capture the listed foods over the month preceding the interview. Responses included:

• never
• 1-3 times per month
• 1 to 7 times per week
• more than once a day (with the option to specify the amount of times per day).

For both the 6- and 12-month FFQs, prompt cards listing foods included in each food group were used at both ages to ensure standardised responses and portion sizes were recorded in household measures and with the aid of food models. Participants were also asked to report frequencies of consumption and amounts of any foods that were not listed in the FFQ if they were consumed once a week or more.

In addition to these FFQs, a 24-hour diet recall was conducted in the whole sample at 6 months and a four-day weighed food diary was conducted among subsamples of 50 mothers of 6 month-olds, and 50 mothers of 12 month-old babies [130, 131]. Both time points also asked about the type and frequency of consumption of any food supplements.

At 3 years old, diet was assessed using an 80-item FFQ administered by research nurses to the main caregiver (usually the mother [132]). As with the FFQ in infancy, the food list was compiled from a variety of sources including:

• a review of dietary intake data from a nationally representative sample of children aged 3 years [133]
• the SWS infants [129]
• the SWS adults [125]
• 3-year-old children in the Avon Longitudinal Study of Pregnancy and Childhood [116].

The food list was refined during the piloting stage.

The average frequency of consumption of food and beverage items over the preceding three months was recoded with the following 11 possible responses:

• (1) never
• (2) less than once/month
• (3) 1-3 times /month
• (4-10) number of times per week
• (11) more than once/day (with the option to specify the amount of times per day).

Prompt cards with lists of examples of foods included in each food group were used. Portion sizes were recorded in household measures. There was space to record frequency of consumption of foods not listed in the FFQ if they were consumed once a week or more. The amount and type of milk, teaspoons of sugar added to food and drinks and dose and frequency of supplements were also recorded.

At the end of the visit at 3 years of age, the caregiver was invited to complete a two-day prospective food diary on behalf of the child which was returned using a prepaid envelope. In this, they recorded all food and drinks consumed by the child from midnight the day following the interview until midnight two days later.

Weight, size, or household measures were used to quantify the amounts consumed. Details on brand name, meal ingredients and cooking methods were recorded. Dietary supplements during this two-day period were also recorded.

The relative validity of the FFQ was assessed in comparison to the two-day food diaries among 892 children in the SWS [132].

The main caregiver also completed an FFQ based on the 3-year FFQ on behalf of the child at age 6-7 years. This asked about frequency of consumption of 84 foods/food groups over the past three months, with the same response options as the 80-item FFQ used previously. The FFQ was followed by some specific questions about milk, sugar, fruit and vegetables, meals away from home, and supplements.

A short FFQ was used to assess diets of children at 8-9 years and 11-13 years. It covered frequency of consumption of 33 foods/food groups over the past three months, with the same response options used previously and was followed by some specific questions about milk, sugar, fruit and vegetables, takeaway meals, and supplements.